The present invention relates to an inverter apparatus adaptable to different specifications, and more particularly to a general-purpose inverter apparatus suitable for driving an induction motor.
Inverter apparatuses capable of controlling the start-up and variable speed operation of an induction motor have widely been used in various applications. To this end, different inverters having various performance and functions depending on various applications have been provided.
Generally shown in FIG. 7, a conventional general-use inverter apparatus is provided with a main circuit 2 which is supplied with three-phase AC power RST via a terminal block 26 from an AC power source 1 and converts the AC power RST to a required variable-frequency variable-voltage three-phase AC power UVW which is then supplied via a terminal block 27 to an induction motor 3 for variable speed driving.
To this end, first, the main circuit 2 is provided with an AC-DC converter 21, a capacitor 22 which smooths a DC voltage from the converter 21, an inverter 23 as a DC-AC converter, a thermistor 24 which senses the temperature of semiconductor elements of the main circuit, and a resistor 25 which senses a main circuit current.
A power supply/sensor unit 4 is provided with a power supply 41 which produces various DC voltages; a sensor unit composed of a current sensor 42 and a voltage sensor 44 which sense a current and a voltage, respectively, in and across the main circuit, and a temperature sensor 45; and a driver 43 which supplies the inverter 23 with a drive signal.
A control/input-output unit 5 is provided with a microcomputer 51 as a main element, a storage unit 52, an operator 56 which acts as an input/output interface, an input circuit 54 and an output circuit 55 which each include a signal connection terminal connected via an isolator unit 53, which includes a photo coupler which provides electrical isolation, using optical signal transmission, as shown.
Thus, the user is able to control the inverter apparatus, using the operator 56 or an external controller connected via the input circuit 54 and the output circuit 55. To this end, the operator 56 is provided with a display unit and an input panel, as shown.
The microcomputer 51 controls the operation of the inverter 23 on the basis of signals from the input circuit 54 and/or the operator 56 in accordance with programs stored therein. The contents of the control by the microcomputer 51 are, for example, determination of an output frequency, and/or voltage generation of a drive signal, and selection of an operation system.
In addition, the contents of the control include processing required for performing a protective operation in accordance with signals from various sensors such as the current sensor 42, voltage sensor 44 and temperature sensor 45; and outputting data which includes the frequency, direction of rotation and current at that time, a factor of protection which has caused the protective operation, if any, to an external controller via the operator 56 and the output circuit 55 and displaying the data.
The operator 56 is mounted on a baseplate of the control/input-output unit 5 or may be set at a position separated from the inverter body. Japanese Patent Application Laid-Open No. JP-A-02-211039 discloses an electric motor which contains a main circuit such as an inverter device with its controller being separated from the main circuit.
This prior art is directed to a servo motor which contains a pack module of a power device, a base driver as its peripheral unit, and a current sensing system. The controller is provided with a control unit with the interfacing between the motor and controller being performed with optical signal transmission.
The above prior art fails to take into consideration diversification of specifications under common use of the main portion of the inverter device, and it is difficult to expand the wide usability of the inverter device sufficiently.
For example, in the conventional inverter apparatus of FIG. 7, the microcomputer 51 controls both the input/output interface and the main circuit 2 of the inverter 23.
The control of the main circuit 2 is inherent in the inverter and not dependent on a customer's requirements.
The control of the input/output interface varies in content depending on a customer's requirement. Thus, when the functions and performance as standard specifications prepared by a manufacturer do not satisfy the customer's requirements, a change of software for the microcomputer, or up to the operator 56 or the input circuit 54 and output circuit 55, are required to be changed as the case may be.
Thus, re-creation of the software for the microcomputer and/or hardware as the input/output interface of the microcomputer may be required depending on the customer's requirements.
In the conventional techniques, the input and output circuits are fixed to the inverter body, so that they cannot be separated from other elements. Thus, the main circuit 2 and the input and output circuits 54 and 55 therefor are provided inevitably in the same place.
The conventional technique of JP-A-02-211039 discloses the use of a main circuit varying depending on the capacity of the electric motor, and the use of the controller as a common element separated from the main circuit. It discloses the technique for separating a power unit and its peripheral unit from a control unit in the controller. Although the conventional technique discloses the control unit side as a new controller which includes the power unit, its peripheral unit and their interfaces, it fails to consider an input/output from/to an external unit to/from the new controller.